Controlling the texture and crystallinity of evaporated lead phthalocyanine thin films for near-infrared sensitive solar cells

Karolien Vasseur, Katharina Broch, Alexander L. Ayzner, Barry P. Rand, David Cheyns, Christian Frank, Frank Schreiber, Michael F. Toney, Ludo Froyen, Paul Heremans

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

To achieve organic solar cells with a broadened spectral absorption, we aim to promote the growth of the near-infrared (NIR)-active polymorph of lead phthalocyanine (PbPc) on a relevant electrode for solar cell applications. We studied the effect of different substrate modification layers on PbPc thin film structure as a function of thickness and deposition rate (rdep). We characterized crystallinity and orientation by grazing incidence X-ray diffraction (GIXD) and in situ X-ray reflectivity (XRR) and correlated these data to the performance of bilayer solar cells. When deposited onto a self-assembled monolayer (SAM) or a molybdenum oxide (MoO3) buffer layer, the crystallinity of the PbPc films improves with thickness. The transition from a partially crystalline layer close to the substrate to a more crystalline film with a higher content of the NIR-active phase is enhanced at low rdep, thereby leading to solar cells that exhibit a higher maximum in short circuit current density (JSC) for thinner donor layers. The insertion of a CuI layer induces the formation of strongly textured, crystalline PbPc layers with a vertically homogeneous structure. Solar cells based on these templated donor layers show a variation of JSC with thickness that is independent of rdep. Consequently, without decreasing rdep we could achieve JSC = 10 mA/cm 2, yielding a bilayer solar cell with a peak external quantum efficiency (EQE) of 35% at 900 nm, and an overall power conversion efficiency (PCE) of 2.9%.

Original languageEnglish (US)
Pages (from-to)8505-8515
Number of pages11
JournalACS Applied Materials and Interfaces
Volume5
Issue number17
DOIs
StatePublished - Sep 11 2013
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Materials Science(all)

Keywords

  • copper iodide (CuI)
  • molecular orientation
  • planar heterojunction
  • polymorphism
  • self-assembled monolayer (SAM)
  • structural templating

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    Vasseur, K., Broch, K., Ayzner, A. L., Rand, B. P., Cheyns, D., Frank, C., Schreiber, F., Toney, M. F., Froyen, L., & Heremans, P. (2013). Controlling the texture and crystallinity of evaporated lead phthalocyanine thin films for near-infrared sensitive solar cells. ACS Applied Materials and Interfaces, 5(17), 8505-8515. https://doi.org/10.1021/am401933d